1. Technical Field
The present disclosure relates to an electric vehicle having left and right rear wheels to be driven by corresponding motors, respectively.
2. Description of the Related Art
There is widely known an electric vehicle having wheels to be driven by corresponding motors, respectively, as one of electric vehicles such as electric automobiles. In this type of electric vehicle, during normal travel of an electric vehicle, a target driving torque is calculated for each motor based on a driving operation amount of a driver, and an output of each motor is feed-back controlled so that an actual driving torque of each motor attains a corresponding target driving torque.
In the above-mentioned type of electric vehicle, braking/driving forces of respective drive wheels can be controlled independently of one another. Thus, the braking/driving forces of drive wheels are controlled independently of a braking/driving operation of the driver as necessary depending on a travel state of the electric vehicle. For example, in Japanese Patent Application Laid-open No. 2015-23753, there is disclosed an electric vehicle configured to calculate a braking/driving force distribution ratio for wheels so that a steering characteristic for the vehicle at the time of turning attains a neutral steering characteristic, and to control a braking/driving force of each wheel based on the braking/driving force distribution ratio.
As widely known in the art, at the time of transitional turning when a vehicle transitions from a traveling straight ahead state to a turning state or from a turning state to a traveling straight ahead state, front wheels, which are steered wheels, are steered and a turning lateral force is generated by the front wheels, to thereby turn around a vehicle body. However, rear wheels try to maintain their earlier movement states, and thus the rear wheels are in a yaw motion with respect to the vehicle body in accordance with a compliance caused by elastic deformation of a rubber bush or the like of a rear wheel suspension. As a result, the rear wheels are in a state of temporarily being steered in a direction opposite to that of the front wheels. After that, the rear wheels are displaced in a yaw direction with respect to the vehicle body so that a longitudinal direction of the rear wheels is returned to a normal position that is directed along a longitudinal direction of the vehicle due to a restoring moment caused by a force generated by elastic deformation of the rubber bush or the like.
The phenomenon described above becomes more conspicuous as a vehicle speed, a change speed of a steering angle of the front wheels, or the compliance of the rear wheel suspension increases. Further, the phenomenon described above becomes more conspicuous in a case of a vehicle in which a suspension member is elastically coupled to the vehicle body and an inner end of a suspension arm is elastically coupled to the suspension member compared to a case of a vehicle in which the inner end of the suspension arm is elastically coupled to the vehicle body. Further, the phenomenon described above is not limited to the time when the vehicle is turning, but also arises, for example, under a situation in which the vehicle receives a cross wind after passing through a tunnel, and the vehicle body is inclined. When the phenomenon described above arises conspicuously, degradation in steering stability due to a change in turning angle of the rear wheels, which is caused along with turning of the vehicle body, cannot be avoided.
In the electric vehicle disclosed in Japanese Patent Application Laid-open No. 2015-23753, the braking/driving force distribution ratio for wheels is calculated as a distribution ratio necessary for causing the steering characteristic of the vehicle at the time of turning to attain the neutral characteristic. Thus, also in the electric vehicle disclosed in Japanese Patent Application Laid-open No. 2015-23753, degradation in steering stability due to a change in turning angle of the rear wheels, which is caused along with turning of the vehicle body due to the phenomenon described above, cannot be avoided.